Polymethine dyes are generally recognized to be those which include at least two nuclei linked through a conjugated methine linkage. The two nuclei can both be basic electron donating nuclei, such as those found in cyanine dyes, acidic electron accepting nuclei, such as those found in oxonol dyes, or one nucleus can be a basic electron donating nucleus and the other an acidic electron accepting nucleus, such those found in merocyanine dyes.
The state of the art relevant to the polymethine dyes of this invention can best be illustrated by reference to merocyanine dyes. Merocyanine dyes contain a chromophore formed by an acidic electron accepting terminal nucleus and a basic electron donating nucleus joined through a methine chain. In so-called zero methine merocyanine dyes there are two methine groups linking the nuclei, but one linking methine group lies in the basic nucleus while the second linking methine group lies in the acidic nucleus. Thus, there are no methine groups separating the nuclei. Homologues of the zero methine merocyanine dyes are those which contain two, four, or a higher even number of methine groups joining the terminal acidic and basic nuclei.
The acidic electron accepting terminal nucleus of a merocyanine dye can be either heterocyclic or acyclic. When the acidic terminal nucleus is acyclic it takes the form of a methylene group which is disubstituted with two strong electron withdrawing groups. The most commonly employed strong electron withdrawing groups are cyano, sulfo, and carbonyl groups, where the latter includes carboxylic acid and ester as well as acyl groups. Acyclic acidic electron accepting terminal nuclei of merocyanine dyes are illustrated by
(R-1) Collins et al U.S. Pat. No. 2,411,507,
(R-2) Kendall et al U.S. Pat. No. 2,511,210,
(R-3) Kendall et al U.S. Pat. No. 2,693,472,
(R-4) Edwards et al U.S. Pat. No. 2,721,799,
(R-5) Kofron et al U.S. Pat. No. 4,439,520, and
(R-6) Gunther et al U.S. Pat. No. 4,576,905.
Merocyanine dyes are known to serve a variety of uses. In one application of particular interest merocyanine dyes can be incorporated in ultraviolet responsive imaging systems. Since ultraviolet light is both more energetic and capable of absorption with simpler molecular resonance structures than visible light, it is not surprising that there are a variety of known imaging materials which respond to ultraviolet, but not visible light. The sensitivity of these imaging systems can be extended into the visible portion of the spectrum by incorporating a dye, referred to as a photosensitizer. Merocyanine dyes have been extensively employed as photosensitizers.
Photographic silver halide emulsions are illustrative of imaging systems known to employ merocyanine dyes as photosensitizers. The radiation sensitive silver halide grains present in photographic emulsions exhibit very limited absorption of radiation of wavelengths extending into the visible spectrum. However, with a merocyanine dye adsorbed to the grain surfaces, the emulsions are highly responsive to visible light. The merocyanine dye absorbs exposing photons and transfers either energy or an electron to the grain. All of the patents cited above disclose this photographic utility for merocyanine dyes.
A variety of photographic imaging systems are known wherein a hardenable organic component containing ethylenic unsaturation sites is relied upon for image formation. The organic component undergoes photoinduced addition reactions, typically either polymerization or crosslinking, at the ethylenic unsaturation sites which produce hardening and allow image discrimination to be achieved.
It is common practice in preparing these compositions to employ coinitiators. One of the coinitiators is a photosensitizer. Photosensitizers are relied upon to capture photons of exposing radiation. The remaining coinitiator is referred to as an activator. The activator is not relied upon to respond directly to exposing radiation, but rather adjacent activator and photosensitizer molecules react, following excitation of the latter by photon capture, causing release by the activator of a free radical which in turn induces immobilizing addition reactions at sites of ethylenic unsaturation. The use of merocyanine dyes as photosensitizers in such imaging systems is illustrated by
(R-7) Specht et al U.K. Pat. No. 3,083,832A,
(R-8) Research Disclosure, Vol. 200, December 1980, Item 20036, and the following four commonly assigned copending patent applications:
(A) Farid et al U.S. Ser. No. 933,712, filed Nov. 21, 1986, titled Dye Sensitized Photographic Imaging System;
(B) Farid et al U.S. Ser. No. 933,658, filed Nov. 21, 1986, titled Negative Working Photoresists Responsive To Shorter Visible Wavelengths And Novel Coated Articles
(C) Farid et al U.S. Ser. No. 933,660, filed Nov. 21, 1986, titled Negative Working Photoresists Responsive To Longer Visible Wavelengths And Novel Coated Articles
(D) Farid et al U.S. Ser. No. 933,657, filed Nov. 21, 1986, titled Enhanced Imaging Composition Containing An Azinium Activator
The following illustrate known compounds containing isocyano groups:
(R-9) U. Schollkopf, "Recent Applications of .alpha.-Metalated Isocyanides in Organic Synthesis", Agnew. Chem., Int. Ed., 1977, 16, 339-422. Note particularly compounds 9, 16, 17a, 17b, 18, 19, 32, and 34.
(R-10) R. H. Hall et al, "Synthesis of C-Glycosyl Compounds. Part 1. Reaction of Ethylisocyanoacetate with 2,3,5,6-Di-O-isopropylidene-D-mannono-1,4-lactone", J. Chem. Soc., Perkin Trans. 1, 1977, 743-753. Note particularly compounds 6, 7, 11, and 12.
(R-11) C. Herdeis et al, "Heterocyclic Substituted Amino Acids via .alpha.,.beta.-Dehydroamino Acid Derivatives. Studies on Amino Acids", Heterocycles, 1983, 20, 2163-2167. Note particularly compounds 3a and 3b.
(R-12) C. Herdeis et al, "Platin(II)-Komplexe Von Vinylogen Aminoisocyanides", Chem. Ber., 1983, 116, 3205-3211. Note particularly compounds 1a and 1c.
(R-13) Schollkopf et al, "Syntheses with .alpha.-Metalated Isocyanides, XLIV. Note on .beta.-Dimethylamino-.alpha.-isocyanoacrylates and Their Use in Heterocyclic Chemistry", Justus Liebigs Ann. Chem., 1979, 1444-6. Note particularly compound 3.
(R-14) Hoppe, ".alpha.-Metalated Isocyanides in Organic Synthesis", Angew. Chem., Int. Ed., 1974, 13, 789-804. Note particularly compounds 143, 145a, and 145b.
(R-15) I. Hoppe and U. Schollkopf, "Synthesis and Biological Activities of the Antibiotic B 371 and its Analogs", Justus Liebigs Ann. Chem., 1984, 600-607.